Radio signaling means



April 2, 1929- D. G. LITTLE ET AL 1,707,271

RADIO SIGNALING MEANS Filed Nov. 22. 1926 lli WITNESSES i INVENTORS 55% y p DOn /OGL/ffle (Q A A/af/van fipsfibaugh. W: BY

ATT'ORNEY Patented Apr. 2, 1 929.

UNITED STATES PATENT; orrlcs.

DONALD G. LITTLE, F EDGEWOOD, AND NATHAN C. DEFIBAUGH, 0F FORREST HILLS, PENNSYLVANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC AN D MANUFACTURING comPANY, A CORPORATION or PENNSYLVANIA.

' aAmo SIGNALING MEANS.

HEISSUED Application filed November 22, 1926. Serial'No. 149,821.

This invention relates to radio-frequency systems of communication and particularly to radio-telegraph systems.

lt has been customary, in some radio-telea graph systems, to generate continuous radiofrequency Waves and interrupt them at a frequency above the keying frequency. The device used for interrupting the continuous waves, usually called a chopper, includes a to mechanical device driven by a motor which requires more power than even a large Vacuum tube. Moreover, the chopper is a noisy apparatus which can, and frequently does, disturb the operators at the sending station.

The signal received from a station including a chopper is harsh and unpleasant to listen to. Such a signal cannot be as easily read as one which is a musical note. Experience shows that a signal, so faint that to it can barely be hard, is more often perceived if musical than if harsh. I

It is an object of the present invention to produce a device for modulating the radiofrequency waves, which shall produce an audio frequency above the keying frequency. The modulation preferably should be complete, causing no actual interruption but bringing the radio-frequency amplitude to zero, for an instant only, once an audio cycle. The device can, if desired, be adjusted to produce an interruption at each cycle but, if this is done, the note begins to lose its musical character.

It is a further object of our invention to produce a device for modulating the radiated waves which shall be quiet in operation and shall require only a small amount of power.

It is a further object of our invention to produce a device for modulating the radiated waves which shall give a musical note in the receiving instruments.

It is a further object of our invention to produce a device for modulating the radiated waves which shall not cause severe strains in the tubes of the sending system.

It is a further object of our invention to provide a keying system by means of which a blocking potential may be impressed upon the tubes when radiation is to be prevented.

It is a further object of our invention to provide such a keying system in which the blocking potential used shall not much exceed pedance to current there that necessary to prevent the tubes from oscillating.

It is a further object of our invention to provide akeying system in which abrupt stopping and starting of the oscillations in the several tubes are produced without excessive strain upon the tubes.

It is a further object of our invention to provide a blocking potential for the grids, controlled by a key and supplied directly from the generator which energizes the tubes.

Other objects of our invention will be apparent from the following detailed description and the accompanying drawing in which the single figure and apparatus.

The vacuum tube 1 is connected to an adjustable inductor 2 and a condenser 3 which are associated with it in any known way to constitute an oscillation generator. for the generator is supplied from a big potential direct-current source 4. An alternating-current source may, if preferred, be utilized but, if so, the tubes fed therefrom will be operative during only a part of the time.

A radio-frequency choke coil 5 protects the source 4 from the oscillations generated at the tube 1, and a condenser 6 prevents a short circuit of the direct current of the source 4. If the source 4 be alternating, the condenser 6 must be small enough to resent a large imrom.

The condenser 7 acts as the grid condenser for the tube 1 and is connected, by the usual grid-leak resistor 8, to the negative terminal of the source 4. The connection includes a choke coil 9 which serves to prevent radiofrequency from reaching this source.

The oscillation generator l is associated with an amplifier including a plurality of tubes 11, connected in parallel. The output circuit of the generator 1 is connected, through the condenser 12, to the grids of the tube 11. The generator 1, therefore, serves as a master oscillator for the plurality of tubes 11. The plate circuit of the tubes 11 contains a primary 13, common to all of these tubes. The plate circuit is supplied from the generator 4, and the primary 13 is associated with a secondary 14 by means of whichthe antenna 15 is energized.

The grids of the tubes 11 are provided with is a diagram of the circuits Energy a grid-leak resistor 16 which islseparated from the grids by a radio-frequency choke coil 17. The resistor 16 is connected to thenegative terminal of the source 4 and thus to the filaments of the tubes 11.

The connection between the resistor 16 and the negative terminal of the source, 4 includes a parallel-resonant circuit comprising an inductor 21 and a condenser 22. The parallel resonant circuit is in the grid circuit of a tube 23 and constitutes a part of the feed-back system by means of. which the tube 23 is caused to generate oscillations. The inductor 21 is coupled with an inductor 24 in the plate circuit of the tube 23. The inductance 21 and the capacity 22 are of such magnitude that the oscillations generated by the tube 23 are of audio-frequency.

There may be provided, instead of the audio-frequency generator 23, a generator of super-audio frequency. Such a generator would require arrangements, not shown herem, for rendering the signal perceptible.

Across the terminals of the generator 4 a potentiometer resistor 25 is connected. The

. common connection of thefilaments of the several tubes to the negative terminal of the generator 4 is over a connection 26, adjustable along said potentiometer. A portion of the resistor 25 is thus included in series between the negative terminal of the generator and the filaments.

A key 27 is connected between the adjustable connection 26 and the negative terminal of the potentiometer. The several grid-leaks are also connected at the negative end of the potentiometer.

In the operation of the device, the oscillation generator 1 produces radio-frequency 0scillations from energy supplied by the source 4. The radio-frequency oscillations are impressed over the condenser 12 upon the grids of the plurality of tubes 11. The tubes 11 are supplied with energy from the source 4 which enables them to act as amplifiers controlled by the master oscillator. Radio-frequency oscillations are thus impressed, over the tfinsformer 13-14, upon the antenna 15.

If the potential received by the grids of the tubes 11 were controlled only by the master oscillator, the energy radiated by the antenna would be unmodulated. Unmodulated continuous radiation produces, in the telephones of the receiving sets, only a direct current and, consequently, can not be heard. It has been usual to render the presence of the signal perceptible by interrupting the radiations,

ut in our invention, the radiations are modulated rather than interrupted. This modulation is produced by a change in potential'of the grids of the tubes 11, obtained by superposing anl audio-frequency potential from the generator 23 u on the radio-frequency from the master osci lator 1 and the steady potentials, therefore, assume a characteristic average value in each tube, respectively.

When the key 27 is opened there is added,

to the grid potentials just mentioned, the

drop over the portion of the resistor 25 to the right of the contact 26. The contact 26 is so adjusted that the additional negative potential is su'fiicient to cause each of the tubes to be blocked. Oscillations of all of the tubes, therefore, cease.

It will be observed that the tube 23 does not use energy when it is performing no useful function. It oscillates only when the radiations are being transmitted. It will also be observed that neither the master oscillator nor the amplifiers are consuming energy when the key is open.

At the moment of opening the key 27, the negative potential impressed upon the grid of the tube 1 includes the drop over the are, which tends to form between the contacts of the key. The grid, therefore, becomes sufiiciently negative to render the tube 1 non-conducting. The path over which the are is supplied thus becomes non-conductive, and the arc is extinguished so promptly that it is not possible to perceive that any are ever forms. As soon as the are (which exists only theoretically) is extinguished, the negative potential impressed upon the grid of the tube 1 is only the drop over the right-hand part of the resistor 25. This is sufiicientto prevent the tube 1 from oscillating but is not even approximately as great as the whole negative potential of the generator 4. If the whole potential of the generator 4 were impressed upon the grid 1, serious strains would result, and the life of the tube would be materially shortened.

Similar considerations show that the relation of each of the tubes to the keying device is such as to prevent an arc, and, by the substitution of the potential over a portion of the potentiometer for the whole of the voltage of the generator lessens these strains impressed upon any of the tubes by the keying process.

In an embodiment of our device, actually built, a 50 watt tube has been employed as the tube 23, where, by the methods of the prior art, a chopper driven by a continuously running motor has been employed. In said actual embodiment, the resistor 8 was 5,000 ohms; the, resistor 16 was 3,000 ohms; the potential of the source 4 was 1,000 volts, the potentiometer resistor 25 was 40,000 ohms and the point 26 was so adjusted that the potential drop across the right-hand part of the resistor was some 250 volts.

Although we have specifically described a single embodiment of our invention, it will be readily understood by those skilled in the art that many variations may be made Without departing from the spirit of this invention. We, therefore, do not wish to be limited except as indicated inthe claims or required by the prior art.

We claim as our invention:

1. In a radio sending system, an antenna, means including a master oscillator and an amplifier for impressing a radio-frequency thereon, a grid-leak circuit including a resist-or and a radio-frequency, choke coil for said amplifier and means for impressing aperiodic audio-frequency potential on said grid-leak circuit.

2. In a radio sending system, a master oscillator, an amplifier controlled thereby, an audio-frequency oscillation generator operatively associated with said amplifier to exert an additional control ,thereon and keycontrolled means for impressing a blocking potential simultaneously on both generators.

'3. In a radio sending system, a master oscillator, an amplifier controlled thereby, an-

audio-frequency oscillation generator oper atively associated with said amplifier to exert an additional control thereon and keycontrolled means for impressing a blocking potential on said amplifier and simultaneously on both generators.

4. In a radio transmitting system, a master oscillator comprising a triode, an amplifier comprising a triode, an audio-frequency gen- .erator comprising a triode, connections whereby said amplifier may be jointly controlled by said master oscillator and said audio-frequency generator, a common source of plate potentialfor said triodes, and means whereby a blocking potential may be derived from said common source and applied simultaneously to the grids of said triodes.

5. In a radio transmitting system, a master 'erator comprising a triode, connections whereby said amplifier may be jointly controlled by said master oscillator and said audio-frequency generator, a common source of high potential for the plates of said triodes, a resistor connected in shunt to said source, connect-ions from the grids of said triodes to the negative end of said source,

connections fromthe cathodes of said triodes to an intermediate 2 point on said resistor, whereby said grids are negatively biased with respect to said cathodes, and means for establishing a shuntaround that portion of the resistor which supplies said biasing potential.

7 "In a radio transmitting system, a master oscillator comprising a triode, an amplifier comprising a triode, an audio-frequency generator comprising a triode having an input circuit, connections whereby said amplifier may be controlled by said master oscillator, connections whereby a grid-leak path associated with said amplifier is comprised in said input-circuit, a common source of plate potential for said triodes, means for deriving a negative potential fromsaid source, and

additional means for applying said negative potential at will to the grids of said triodes. In testimony whereof, We have hereunto subscribed our names this 20th day of November, 1926.

DONALD G. LITTLE. NATHAN C. DEFIBAUGH. 

